Wireless communication systems are widely deployed to provide various types of communication such as voice and data. These systems may be based on code division multiple access (CDMA), time division multiple access (TDMA), or some other multiple access techniques. A CDMA system provides certain advantages over other types of systems, including increased system capacity.
A CDMA system may be designed to support one or more CDMA standards such as (1) the “TIA/EIA-95-B Mobile Station-Base Station Compatibility Standard for Dual-Mode Wideband Spread Spectrum Cellular System” (the IS-95 standard), (2) the standard offered by a consortium named “3rd Generation Partnership Project” (3GPP) and embodied in a set of documents including Document Nos. 3G TS 25.211, 3G TS 25.212, 3G TS 25.213, and 3G TS 25.214 (the W-CDMA standard), (3) the standard offered by a consortium named “3rd Generation Partnership Project 2” (3GPP2) and embodied in “TR-45.5 Physical Layer Standard for cdma2000 Spread Spectrum Systems” (the IS-2000 standard), and (4) some other standards. An example non-CDMA system is the GSM system.
Neighboring systems may employ one or more radio access technologies on one or more frequencies. Furthermore, a system may have one radio access technology overlaying another. For example, portions of a GSM system may be overlapped with W-CDMA base stations. It may be desirable for a mobile station communicating on the W-CDMA system to handoff to the GSM system without dropping an active call.
To facilitate such handoff, and to maintain a call on a serving system, a mobile station may be required to periodically search for base stations on alternate frequencies and/or alternate radio access technologies while searching on the serving frequency as well. The W-CDMA specification, for example, provides for a compressed mode, in which gaps in transmission and reception on a serving frequency are introduced, allowing the mobile station to switch frequencies and perform measurements or searching on an alternate frequency while maintaining an active call. However, frequency discontinuity may interfere with a search that is being performed on the serving frequency.
To maintain communication performance on the serving frequency, intra-frequency searching of a minimum level should be maintained. At the same time, overall communication performance requires inter-frequency or inter-Radio Access Technology (inter-RAT) measurements to allow for inter-frequency or inter-RAT handoff, when necessary. Minimum periods between intra-frequency and inter-frequency searches may be prescribed for a system. In addition, or alternately, performance requirements may be prescribed without specifying the search procedure to be performed. The number of cells that a mobile station is able to detect may vary based on the location of the mobile station within the system and the corresponding channel conditions between the various neighbor cells and the mobile station. A mobile station may have a fixed amount of time available to periodically monitor detected cells, including inter-frequency, intra-frequency, and inter-RAT cells. Although the fixed amount of time for searching during subsequent periods may vary, during some periods the time required to search the detected cells for monitoring may exceed the fixed time available.
The performance of a system, including throughput as well as system capacity, relies in part on efficient use of available base stations, including intra-frequency, inter-frequency, and inter-RAT base stations. Thus, searching the detected cells indicated for monitoring should be performed such that any prescribed minimum search periods and/or performance requirements are met utilizing the search time allotted. There is therefore a need in the art for searching neighbor cells within a fixed time duration.